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Why Is the Gelcoat Cracking?

I noticed, while waxing my hull, that there were some vertical cracks underneath the through-hull drain from the sink. Does this mean the through-hull is not installed properly?

I compliment you for waxing your own hull, as that is an excellent way to get a close look at your gelcoat and find cracks and other such imperfections, but even if you don’t do your own waxing, the entire boat needs to be closely inspected at least twice a year. Check around all the windows for any rusting around cleats and other metal. Look closely around all through-hulls and anywhere else the gelcoat is penetrated, as there could be a chance for water to permeate the fiberglass. Inspect every inch of your boat’s exterior, looking for any cracking, anywhere. Detecting things sooner rather than later can save big money in the long run.

About the cracks under the sink drain through-hull. First, if the cracking has not been going on very long, this could be blemishing on the gelcoat. The cause could be a through-hull issue, but it is more likely caused by your dish detergent or other harsh chemicals going down the drain. Always use dish soap that is biodegradable and as mild as possible. Unfortunately, if there is damage, the gelcoat will need to be ground down to the fiberglass, and you will need to look for any chemical damage to the fiberglass beneath. As damage may creep all the way to the through-hull, it may need to be resealed. The next time you have your boat out of the water, fix it. In the meantime, try to seal the spot and be careful about what goes down the drain.